1. Field of the Invention
The subject invention relates generally to a system and method of balancing a state of charge (SOC) of a plurality of cells connected in series.
2. Description of the Related Art
Electric vehicles and hybrid-electric vehicles typically utilize numerous cells (i.e., batteries) for powering electric loads such as drive motors and other electric equipment. These cells are often connected together in a series relationship, as is well known to those skilled in the art, to provide higher voltages.
Due to variations between individual cells, such series-connected cells require periodic balancing, i.e., charge equalization, to maintain a steady voltage. prevent premature failure, and provide maximum power to the load. Various systems and techniques have been developed to address this necessity. For example, active cell balancing methods include charge shunting, where current is shunted around fully charged cells; charge shuttling, where charge is removed from one cell and delivered to another cell; energy converters, where inductors or transformers move energy from a cell or group of cells to another cell or group of cells; and energy dissipation, where charge is removed from the cells with the highest charge.
Particularly, the use of energy converters, such as inductive charge shuttling, to shuttle current between individual cells is commonly used. However, inductive charge shuttling techniques are typically “open loop” techniques, i.e., the current delivered to the cell to be charged is based on the tolerance of the inductor and generally not variable.
As it as advantageous to vary the amount of current provided to the cell based on the current charge of the cell, there remains an opportunity for a method and system for balancing a state of charge of a cell based on the current charge of the cell.